Platform structure

ABSTRACT

An offshore drilling platform includes a massive and heavy caisson surmounted by a lightweight superstructure. The center of buoyancy is above the center of gravity of the platform and the platform can be floated in upright position to a desired location and sunk by introducing ballast, such as sea water, into the caisson. the platform rests on the sea floor and is stable due to its own weight while the lightweight superstructure extends above the sea surface. A drilling platform is provided in fixed position on the superstructure above sea level.

United States Patent 1 1 M0 July 23, 1974 1 PLATFORM STRUCTURE 1 3,472,033 10/1969 Brown 61/46 [76] Inventor: Olva M0, Gronsundveien 94,

Nesbru, l37o-Asker, Norway 3,572,043 3 1971 Clara 3,698,198 10/1972 Phelps [22] 1972 3,708,987 1 1973 Roulet et a1, 61/46 [21] OTHER PUBLICATIONS The Oil and Gas Journal of Sept. 14, 1970 pages 60, [30] Foreign Application Priority Data 61' Sept. 7, 1971 Norway 3325/71 Mar. 16, 1971 Norway Primary Examiner-Jacob Shapiro Nov. 19, 1971 Norway 4282/71 Attorney, Agent, or Firm--Larson, Taylor and Hinds [52] US. Cl. 61/465, 220/18 57] ABSTRACT [51] Int. Cl E02d 17/00, E02d 27/38 An Offshore drilling platform includes a massive and Field Of Search 50, .5, heavy caisson surmounted a superstruc 220/18 ture. The center of buoyancy is above the center of gravity of the platform and the platform can be floated [56] References cued in upright position to a desired location and sunk by UNITED STATES PATENTS introducing ballast, such as sea water, into the caisson. 2,351,509 6/1944 Hammeren 220/18 the platform rests on the sea floor and is stable due to 2,382,171 8/1945 Pomykala 61/46 X its own weight while the lightweight superstructure ex- 2,472,869 6/1949 Travers 61/46-5 X tends above the sea surface. A drilling platform is pro- 218921314 6/ 1959 Hofnsby et 61/46-5 3 vided in fixed position on the superstructure above sea 2,940,266 6/1960 Sm1th 61/465 level 2,990,796 7/1961 Cole et al..... l14/.5 T 3,360,810 1/1968 Busking 114/.5 T 10 Claims, 6 Drawing Figures PATENTEDJUL23l974 sum 1 or 4 PAIENIEBJUmmM SHEEI 30F 4 PAIENTED JU L231974 SHEEI U BF 4 1 PLATFORM STRUCTURE The invention relates to a drilling platform for drilling after and production of natural deposits under the sea. I Conventionally drilling platforms are made completely out of steel. Thus one achieve slender and light structures, which all suffer from substantial weaknesses. The known main types are:

a. Floating platforms which fall outside the scope of this invention.

b. Submersible platforms which stand on the bottom, but which due to their light structure are not suited for greater depths or rough weather districts.

0. J ack-up platforms which due to their slender structure are easily damaged when placed on the bottom.

d. Stationary production platforms which are ground down into the bottom, and thus have the disadvantage that they never can be moved.

The present invention is based on the concept that a platform can be made with a heavy and solid underpart in the shape of a box, and alight, slim upper part which offers little wave resistance, as well as the concept that the platform is shaped such that it as a unit may be used as a floating body during transfer.

Normally it will be natural to shape the underpart as a caisson of concrete. The upper part may be fabricated as a framework of steel or as one or more vertical pipes of concrete and with a cover on the top.

Lifting and lowering of the caisson be effected either by pumping compressed air in or by pumping water out and in. In the first case the caisson walls will mainly receive tension, in the second case pressure. The latter is very favourable if the construction material is concrete. It has furthermore the advantage that the volume of air does not change as the platform goes up or down. Lifting and lowering thus becomes more safe.

Stability during lifting, transport and lowering is achieved, e.g., by always having the centre of gravity below the center of buoyancy. This may be achieved by a suitable shaping of the platform, by making the bottom plate extra heavy or by sand filling in the caisson.

The stability can also be achieved or improved by shaping the working platform as a floating body which can be lowered.

Stability in stationary condition on the bottom of the sea is achieved almost automatically since the wave forces get little hold, at the same time as the lower part of the platform works as a heavy and stable base. The large specific weight of the concrete may in itself provide enough weight, but the stability may be further increased by filling sand in the caisson. The sand may be filled in on the production site and thus in practice constitute a part of the platform, or it may be filled in after the platform is placed on the operation site.

The teeth can be pressed down into the bottom. The

teeth have the advantage that the cross section is largest at the top where the strain is largest both from normal forces and sheer forces. A conical form of the teeth will contribute to the platform being easier to get up a am. Normally the concrete caisson should be built up of vertical cells. If the cells are round with spherical shellformed terminations at both ends, a shape is achieved which is especially suited to withstand large pressure forces.

Besides working as a drilling platform the construction can work at a platform for other needs, above all for production of a field, but also for industry and for mooring of ships.

The caisson can be built as a storage tank for natural resources or for waste products.

For a better understanding of the invention it will be described further by means of examples.

FIGS. 1-6 are diagrammatic elevation views of six alternative embodiments of the invention.

FIG. 1 shows the platform standing on the bottom of the sea. The underpart consists of the concrete caisson l, the upper part of a framework of steel 2. The working platform is indicated by 3, and the drilling tower by 4. The drilling takes place through a well 5. This is not necessary but offers a practical advantage in that it can collect waste of oil, and protects the drilling operations against current, wind, ice and waves.

FIG. 2 shows a platform completely of concrete. The platform is built up of vertical cells 8 10, with bottom plate 7 and top plate 11. A cell 10 is used as a well for the drill 12 with accessories, while the others 8 9 may be filled with oil, water, sand or air as required.

FIG. 3 shows a variant of FIG. 2. only one cell 10 is here carried up over the surface of the water, and it is made conical in order to furtherdecrease the surface of attack for the waves. The figure shows an example of shaping of the half spherical-formed endsurfaces of the cells.

FIG. 4 shows an embodiment with a skirt 13 to damp the erosion. The embodiment shows further a caisson 16 mounted on three points and thus statically determined. The upper part consist of a platform 14 which rests on a steady framework 15, which again rests on the caisson.

FIG. 5 shows an embodiment with teeth 18.

FIG. 6 shows another embodiment with a small lower part 21.

A platform according to the invention is virtually without movable parts. In both floating and stationary state, it is nevertheless stable and is, in addition independent of special anchorings. The parts which form the base are particularly stable, which is particularly important when placing on the bottom of the sea. All the work, including the set up of the majority of the equipment, can normally take place at shore, such that only the very placing must be done at the field. All this makes the platform rugged, mobile and usable to a degree not known for any other known types.

The caisson should have vertical or almost vertical walls, as these thus can be covered by a sliding formwork in floating position. By letting the caisson sink down as the casting advances, there is practically no limit for the size of the caisson, which it is possible to make.

The platform is towed normally during transport, but it may also be equipped with its own propulsion machinery.

The vertical tubes which on several of the embodiments, goes from the working platform to the bottom of the sea, give many possibilities for the drilling operations. The tube works as a shielding against the natural forces and this easies the drilling. The tube may also be filled with sand, and one will then be able to drill approximately as on shore. Such a sand filling will also improve the static conditions for the platform. The tube may also be sealed against the bottom and pumped empty if the bottom conditions permit. The drilling may then take place on dry sea bottom, and the tube itself may possibly be used as a drilling tower. When the bottom conditions are bad, the tube may be provided with a sluice, and filled with gas under pressure, such that the outer water pressure is outbalanced.

It will immediately be understood that the embodiments of the invention shown on the drawings, and described above, are only meant to illustrate the inventive thought, and that this can be varied in a series of ways, within the idea of the invention. A platform according to the invention offers a series of advantages, in preference to the conventional. The greatest is that while conventional steady platforms become unreasonably expensive when used on depths over 100 metres, the new platform is economical down to the largest depths, which to-day are of current interest for oil drilling. The

set-up work at the site is further limited to a minimum,

which is of vital importance in districts of hard weather. Other advantages are: Possibilities for cheap storage of oil, short building time, little maintenance and high mobility.

I claim:

1. An offshore drilling platform comprising, in combination; a massive heavy caisson, comprising a plurality of contiguous vertical elongated cylindrical cells, at least one but not all of the cells lengthened to above sea level to form a support for a deck section, a deck section rigidly mounted on the supporting cell or cells, the non-lengthened cells located a substantial distance below the deck section so that the top of said nonlengthened cell or cells is at a substantial depth below the surface of the sea when sunk, the whole structure being constructed and arranged such that the center of buoyancy of the platform is located above the center of gravity thereof whereby the entire platform floats in water in an upright position and such that when said cell or cells is filled with ballast, said platform sinks with said caisson resting on the sea bottom such that the platform can stand stably on the sea bottom of its own weight with said lengthened cell or cells including said drilling section above sea level.

2. An offshore drilling platform according to claim 1 wherein the height of said platform, up to said deck section is more than 300 meters.

3. A platform according to claim 1 wherein said caisson comprises vertical concrete chambers.

4. A platform according to claim 1 wherein said platform has substantially vertical sidewalls.

5. A platform according to claim 1 wherein said platform includes a well extending lengthwise thereof to accomodate a drill extending from said drilling platform to the sea bed.

6. A platform according to claim 5 further including pumping means for emptying said well.

7. A platform according to claim 5 including a drilling tower mounted on said deck section, and a drill extending from said drilling tower through said well.

8. A platform according to claim 1 wherein the bot tom of said caisson is provided with teeth projections for penetrating the sea bed.

9. A platform according to claim 1 wherein said caisson comprises a plurality of vertical chambers.

10. A platform according to claim 9 wherein each of said chambers is cylindrical, the top and bottom ends thereof being spherical. 

1. An offshore drilling platform comprising, in combination; a massive heavy caisson, comprising a plurality of contiguous vertical elongated cylindrical cells, at least one but not all of the cells lengthened to above sea level to form a support for a deck section, a deck section rigidly mounted on the supporting cell or cells, the non-lengthened cells located a substantial distance below the deck section so that the top of said nonlengthened cell or cells is at a substantial depth below the surface of the sea when sunk, the whole structure being constructed and arranged such that the center of buoyancy of the platform is located above the center of gravity thereof whereby the entire platform floats in water in an upright position and such that when said cell or cells is filled with ballast, said platform sinks with said caisson resting on the sea bottom such that the platform can stand stably on the sea bottom of its own weight with said lengthened cell or cells including said drilling section above sea level.
 2. An offshore drilling platform according to claim 1 wherein the height of said platform, up to said deck section is more than 300 meters.
 3. A platform according to claim 1 wherein said caisson comprises vertical concrete chambers.
 4. A platform according to claim 1 wherein said platform has substantially vertical sidewalls.
 5. A platform according to claim 1 wherein said platform includes a well extending lengthwise thereof to accomodate a drill extending from said drilling platform to the sea bed.
 6. A platform according to claim 5 further including pumping means for emptying said well.
 7. A platform according to claim 5 including a drilling tower mounted on said deck section, and a drill extending from said drilling tower through said well.
 8. A platform according to claim 1 wherein the bottom of said caisson is provided with teeth projections for penetrating the sea bed.
 9. A platform according to claim 1 wherein said caisson comprises a plurality of vertical chambers.
 10. A platform according to claim 9 wherein each of said chambers is cylindrical, the top and bottom ends thereof being spherical. 